QoS control method for transmission data for radio transmitter and radio receiver using the method

ABSTRACT

A radio transmitter/receiver having a QoS control unit for outputting the transmission data in order taking the quality of service (QoS) into consideration. In the case where the information transmission rate for a radio section is not lower than a threshold value, the QoS control operation of the transmission data is omitted, and the transmission data are output in the order of input. In the case where the information transmission rate for the radio section is lower than the threshold value, on the other hand, the QoS control mode is switched in accordance with the information transmission rate for the radio section.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a radio transmitter/receiver, orin particular to the QoS (quality of service) control of thetransmission data in a radio transmitter/receiver.

[0002] In recent years, IP (internet protocol) has come to be employedfor more and more networks with the extension of the internet and aninexpensive IP communication network. In the IP network, data aredelivered to a destination from a transmitter in accordance with the IP.The IP is a protocol for a network layer (third layer) in the OSIreference model. Upper protocols include a TCP (transmission controlprotocol) and a UDP (user datagram protocol) in the transport (fourth)layer. The TCP and UDP have the function of acting as an intermediarybetween the IP and an application program. The protocols lower than IP,on the other hand, include those for a data link layer (second layer)and a physical layer (first layer). The Ethernet defined under IEEE802.3and the radio LAN defined under IEEE802.11 are examples.

[0003] The radio LAN technique is used also for radio access to realizea subscriber network by radio, and various applications (including theWEB access, IP telephone and TV conference) have become possible toexecute with the IP network in both a radio system and a wire system.Applications include those requiring the real-time operation such asvideo distribution and IP telephone, and those requiring no real-timeoperation such as the file data downloading.

[0004] In the IP network, on the other hand, in order to deliver timecritical data such as the voice and video to the destination devicewithin a predetermined time, the QoS control operation is used in whichthe transmission data are classified according to traffic type in thenetwork and transferred by each node taking the QoS into consideration.The QoS control technique well known for the IP network includes, forexample, MPLS or DiffServ at the network layer level and IEEE802.1D atthe data link layer level.

[0005] The disclosure of IEEE802.1D is hereby incorporated by reference.

[0006] MPLS is described, for example, in “Multipleprotocol LabelSwitching Architecture” by E. Rosen et al., RFC3031, pp. 8-11, January2001. DiffServ, on the other hand, is described, for example, in “AnArchitecture for Differentiated Services” by S. Blake et al., RFC2475,pp. 10-18, December 1998.

[0007] IEEE802.1D concerns a QoS control technique for the wire LAN, andimplemented in such a manner that a priority indication label isattached to the header of the Ethernet frame, for example, and eachbridge unit sets the transfer frames in a queue in the order ofpriority. According to IEEE802.1D, as shown in the priorityclassification of FIG. 13, for example, the traffic is divided intoseven types 311 including “network control”, “voice”, “video”,“controlled load”, “excellent effort”, “best effort” and “background”,and the priority 312 is defined for each traffic type.

[0008] The “network control” is the traffic required for maintaining thenetwork environment and handled with the highest priority “7”. The“voice” and “video” which are limited in delay time and jitters, on theother hand, have the next highest priority of “6” and “5”, respectively,following the network control. These traffic types are followed by the“controlled load”, the “excellent effort”, the “best effort” and the“background” in that order of priority. The priority of the normal LANtraffic including the mail and WEB are set in the category of “besteffort”.

[0009] In radio communication, on the other hand, an adaptive modulationsystem has been proposed in which high-speed communication isestablished under satisfactory conditions of the radio section, whilethe communication rate is reduced in a deteriorated radio environment.Refer, for example, to “Symbol Rate and Modulation Level-ControlledAdaptive Modulation/TDMA/TDD System for High-Bit-Rate Wireless DataTransmission” by Toyoki Ue et al., IEEE Trans. on Vehicular Technology,Vol. 47, November 1998, the disclosure of which is hereby incorporatedby reference, and JP-A-10-93650, JP-A-2002-290246 and JP-A-2002-199033.

SUMMARY OF THE INVENTION

[0010] A system employing the adaptive modulation for radiocommunication poses the problem that the information transmission rateundergoes a change depending on the conditions of the radio section.Thus, demand has arisen for a QoS control technique which can maintainthe required network environment even in the case where the informationtransmission conditions undergo a change in the radio section.

[0011] Assume that the conventional QoS control technique for the wireLAN described above is used for the radio communication system ofadaptive modulation type for the radio section. The radio transmitterreads the label information added to the header or the transmissiondata, and classifies the transmission data according to the labelinformation. This process of transmission data classification consumesconsiderable length of time, and an increased delay time of datatransmission reduces the throughput.

[0012] In the case where the information transmission rate for the radiosection is higher than the transmission rate of the transmission datasupplied to the radio transmitter, no waiting time basically occurs forthe transmission data in the radio transmitter. In the conventional QoScontrol technique, however, all the transmission data are classified onthe assumption that the transmission waiting time occurs on the outputline. Therefore, the QoS control unit requires a high-speed processingcircuit, thereby leading to the problem of a high system cost.

[0013] Accordingly, an object of this invention is to provide a QoScontrol method and system used with a radio transmitter/receiver, inwhich the delay time of data transmission under QoS control is shortenedand the data throughput can be improved.

[0014] Another object of the invention is to provide a radiotransmitter/receiver in which the delay time of the data transmissionunder QoS control is shortened and the data throughput can be improved.

[0015] Still another object of the invention is to provide a radiotransmitter/receiver of adaptive modulation type, in which the delaytime of the data transmission under the QoS control is shortened and thedata throughput is improved.

[0016] According to one aspect of the invention, there is provided a QoScontrol system used for a radio transmitter/receiver, comprising:

[0017] a QoS control unit for supplying the transmission data to themodulation unit of the radio transmitter/receiver in the order takingthe QoS into consideration; and

[0018] a determining unit connected to the QoS control unit fordetermining whether the QoS control operation of the transmission datais required or not in accordance with the information transmissionconditions in the radio section;

[0019] wherein the QoS control operation of the transmission data isselectively performed by the QoS control unit in accordance with theinformation transmission conditions in the radio section.

[0020] One preferable feature of the invention lies in that the QoScontrol unit has a first operation mode for outputting the transmissiondata in the order of input thereto and a second operation mode foroutputting the transmission data in the order taking the QoS intoconsideration, the first and second operation modes being adapted to beswitched in accordance with the information transmission conditions inthe radio section.

[0021] Another preferable feature of the invention lies in that the QoScontrol unit includes a comparator for comparing the informationtransmission rate for the radio section with a predetermined thresholdvalue, and in the case where the information transmission rate for theradio section is lower than the predetermined threshold value, the QoScontrol operation is switched to the second operation mode, while in thecase where the information transmission rate for the radio section ishigher than the predetermined threshold value, on the other hand, theQoS control operation is switched to the first operation mode.

[0022] Still another preferable feature of the invention lies in thatthe QoS control unit has a plurality of QoS control modes, and the QoScontrol operation for the transmission data is switched between aplurality of the QoS control modes in accordance with the informationtransmission rate for the radio section.

[0023] Yet another preferable feature of the invention lies in that theQoS control unit has a QoS control mode table for defining the relationbetween the range of the transmission rate for the radio section and theQoS control mode applicable to the transmission data, and the QoScontrol mode applicable to the transmission data is determined inaccordance with the information transmission rate for the radio sectionwith reference to the QoS mode table.

[0024] A further preferable feature of the invention lies in that theQoS control unit has a classification table corresponding to a specifiedQoS control mode defined in the QoS control mode table, theclassification table defines the class of each transmission datacorresponding to the value of specific header information included inthe transmission data, and the QoS control unit determines the class ofthe transmission data in the specific QoS control mode with reference tothe classification table.

[0025] According to an embodiment of the invention, in the case wherethe information transmission rate for the radio section is not lowerthan a predetermined threshold value, the QoS control operation for thetransmission data is omitted, and therefore the data transmission withminimized transmission delay in the QoS control unit is made possiblefor an improved data throughput. Also, the omission of the QoS controloperation requiring a high speed makes possible a comparativelyinexpensive hardware configuration of the radio transmitter.

[0026] According to an embodiment of the invention, the QoS controloperation for the transmission data is carried out in the case where theinformation transmission rate for the radio section decreases below thepredetermined threshold value. In this case, a time margin is generatedfor supplying the transmission data to the radio transmission circuit,and therefore the transmission delay due to the QoS control process hasa smaller effect on the throughput. Also, the aforementioned time marginincreases with the decrease in the information transmission rate for theradio section. Therefore, the QoS control operation is also madepossible by a QoS control unit having a plurality of QoS control modeswhich are switched in accordance with the information transmissionconditions in the radio section in such a manner that a more complicatedQoS control operation is used with the decrease in the transmissionrate.

[0027] Other objects, features and advantages of the invention willbecome apparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a block diagram showing a radio transmitter/receiveraccording to an embodiment of the invention.

[0029]FIG. 2 is a detailed diagram showing the QoS control unit 11 inFIG. 1.

[0030]FIG. 3 is a flowchart showing the operation of the classificationunit 110 shown in FIG. 2.

[0031]FIG. 4 is a flowchart showing the operation of the read controlunit 113 shown in FIG. 2.

[0032]FIG. 5 is a diagram showing an example of communication to whichthe radio transmitter/receiver according to the invention is applicable.

[0033]FIG. 6 is a diagram showing an example of the header contents ofan IP packet exchanged between the client 20B and the server 20A shownin FIG. 5.

[0034]FIG. 7 is a diagram showing a detailed format of an IP header 43.

[0035]FIG. 8 is a diagram showing a detailed format of a TCP header 41.

[0036]FIG. 9 is a diagram showing a detailed format of a UDP header 42.

[0037]FIG. 10 is a diagram showing a classification table 32 showing theclasses corresponding to the port numbers.

[0038]FIG. 11 is a diagram showing a QoS control mode table 33.

[0039]FIG. 12 is a diagram showing a classification table 34 for thecontrol policy A.

[0040]FIG. 13 is a diagram for explaining the priority (class) definedunder IEEE802.1D.

[0041]FIG. 14 is a diagram showing a class-wise band assignment table35.

[0042]FIG. 15 is a diagram showing a frame format under IEEE802.11a.

[0043]FIG. 16 is a block diagram showing a configuration of a radiotransmitter/receiver of adaptive modulation type using the QoS controloperation according to an embodiment of the invention.

[0044]FIG. 17 is a diagram showing a FWA (fixed wireless access) systemconfiguration using the QoS control operation according to theinvention.

[0045]FIG. 18 is a diagram showing an example of the process of P-Pconnection between a base station and a terminal station.

[0046]FIG. 19 is a diagram showing an example of the correspondencetable between the receiving level and the modulation scheme used in apropagation path estimation unit.

[0047]FIGS. 20A, 20B, 20C are diagrams showing an example of the datatransmission frame format.

DESCRIPTION OF THE EMBODIMENTS

[0048] Embodiments of the invention will be explained in detail belowwith reference to the accompanying drawings, in which similar componentparts are designated by the same reference numerals, respectively.

[0049]FIG. 1 is a block diagram showing a configuration of a radiotransmitter/receiver according to an embodiment of the invention. Theradio transmitter/receiver comprises a data input/output unit 10, a QoScontrol unit 11 making up the essential part of the invention, an accesscontrol unit 12 for receiving the transmission data subjected to QoScontrol from the QoS control unit 11, a modem 13, a RF unit 14, anantenna unit 15, an internal bus 16 and a control unit 20. The modem 13is of adaptive modulation type with the data transmission rate variabledepending on the conditions in the radio section.

[0050] The QoS control unit 11 performs the selective QoS controloperation on the transmission data supplied from the data input/outputunit 10, in accordance with the the radio transmission rate of theinformation input through a signal line L13 from the modem 13, andoutputs the transmission data to the access control unit 12 through thesignal line L11. The transmission data is output from the access controlunit 12 to the modem 13, and after being modulated in the modem 13,converted into a radio frequency at the RF unit 14 and transmitted tothe radio section from the antenna unit 15.

[0051] The radio signal received from the antenna unit 15, on the otherhand, after being frequency-converted by the RF unit 14, is demodulatedby the modem 13 according to a demodulation scheme corresponding to themodulation scheme for transmission, and input to the access control unit12 as received data. The access control unit 12 has the function as aformatter for deleting the sync bits of the demodulated received dataand/or demultiplexing the demodulated received data. The received dataare transferred from the access control unit 12 through the internal bus16 to the data input/output unit 10 and output as the receivedinformation.

[0052] The control unit 20 controls the whole of the radiotransmitter/receiver. The control unit 20, the QoS control unit 11 andthe access control unit 12 are shown as individual elements.Nevertheless, the QoS control unit 11 and the access control unit 12 maybe integrated with each other, so that the functions of the respectivecontrol units may be implemented either by the software executable on asingle processor or by the software executed on the control unit(processor) 20.

[0053] The access control unit 12 may be so configured as to generatethe transmission data of the format defined by, for example, IEEE Std802.11a, page 7, § 17.3.2 PLCP frame format. FIG. 15 shows the PLCPframe format. In FIG. 15, the transmission rate (modulation scheme) ofthe DATA field is defined by the RATE bits of the SIGNAL field. TheSIGNAL field is transmitted at a fixed rate.

[0054]FIG. 2 is a diagram showing the QoS control unit 11 in detail.

[0055] The QoS control unit 11 includes a buffer memory 111 fortemporarily holding the transmission data supplied from a datainput/output unit 10, a classification processing unit 110, atransmission buffer memory 112 with transmission queues 112-0 to 112-nformed by class, a read control unit 113 for reading the transmissiondata from the transmission buffer memory 112 in the order set taking QoSinto consideration and outputting the transmission data to the accesscontrol unit 12 through a signal line L11, and a memory 30 for the QoScontrol information table accessed by the classification processing unit110 and the read control unit 113.

[0056]FIG. 3 is a flowchart showing the operation (the prioritydetermining process 1110) of the classification processing unit 110.

[0057] The classification processing unit 110 determines whether thetransmission data has arrived at the buffer memory 111 or not (step1111), and upon arrival of the transmission data, checks the radiotransmission rate X of the information input through the signal line L13from the modem 13 (step 1112). In the case where the informationtransmission rate X for the radio section is not lower than apredetermined threshold valve A, the QoS control processing is omitted,and the transmission data is stored (set) in the default transmissionqueue 112-0 (step 1115). The threshold value A indicates, for example,the maximum transmission rate of the transmission data input from thedata input/output unit 10. The transmission rate X not lower than thethreshold value A indicates a state in which the transmission data inthe transmission buffer 112 develops no congestion (waiting time).

[0058] According to this invention, only in the case where theinformation transmission rate X for the radio section is smaller thanthe threshold value A, i.e. only in the the case where the transmissiondata develops a congestion, the QoS control operation is executed. Inthis case, the classification processing unit 110 determines the class pof the transmission data with reference to the QoS control informationtable memory 30 (step 1113), and stores the transmission data in thetransmission queue 112-p corresponding to the class p (step 1114). Afterone transmission data is stored in the transmission queue 112-0 or112-p, the process returns to step 1111 to repeat a similar operationfor the next transmission data.

[0059] According to this embodiment, the QoS control operation isperformed independently of a remote station. The informationtransmission rate X for the radio section, therefore, is derived fromthe modulation scheme selected by a propagation path estimation means(not shown) (see the propagation path estimation means 11-1 in FIG. 16)of the local station. Once the modulation scheme is estimated, theinformation transmission rate X is determined from the table of FIG. 19showing the correspondence between the receiving level and themodulation scheme. As an alternative, the QoS control operation may beperformed in accordance with the remote station. In this case, theinformation transmission rate of the local station and the modulationscheme are determined from the information transmission rate X includedin the received data.

[0060]FIG. 4 is a flowchart showing the operation of the read controlunit 113 (the read control processing 1130).

[0061] The read control unit 113 determines whether data transmission ispossible or not from the state of the enable signal output to the signalline L12 from the access control unit 12 (step 1131). In the case wheredata transmission is possible, the transmission data is read inaccordance with the band guaranteed for each class from the transmissionqueue of the transmission buffer memory 112 and output to the accesscontrol unit 12 through the signal line L11 (step 1132).

[0062] The token bucket (or leaky bucket) scheme is known for readingthe transmission data in accordance with the band guaranteed by class.See for example “A scalable Architecture for Fair Leaky-Bucket Shaping”,Jennifer Rexford et al., IEEE1997. According to this scheme, eachtransmission queue has tokens corresponding to the band, andtransmission is permitted as long as at least transmission data lengthtokens are held. The tokens are supplemented in accordance with theguaranteed band at regular time intervals and consumed in accordancewith the data transmission amount. The read control unit 113 supplementsthe tokens by reference to the class-wise band assignment memory area inthe QoS control information table memory 30 at regular time intervals,and consumes the tokens when reading the data.

[0063] According to this invention, the classification process can beexecuted in step 1113 of FIG. 3 in accordance with the method definedby, for example, IEEE802.1D described above. The classificationprocessing unit 110 reads the priority indication label included in thetransmission data or the header portion thereof, and determines thepriority (class) p of each transmission data. The transmission data isthus set in the transmission queue 112-p of the class corresponding tothe priority. In this method, however, the priority indication label isadded to all the transmission data as a prerequisite. In the case wherethe priority indication label is not added to the transmission data,therefore, the QoS control operation cannot be performed.

[0064] In view of this, according to the first embodiment of theinvention, the class of each transmission data can be determined byusing the classification table defining the class corresponding to thevalue of specific header information extracted from the header portionof the transmission data, even in the case where the priority indicationlabel is not attached to the transmission data.

[0065] An embodiment in which the class is determined from the portnumber as header information will be explained below.

[0066]FIG. 5 shows an example of communication using a radiotransmitter/receiver according to the invention, in which a radio client20B accesses the Web page on a server 20A using a Web browser.

[0067] The radio client terminal 20B is assigned an IP address“172.20.100.34”, for example, and equipped with TCP and UDP above the IP22B as a transport layer 23B on the one hand, and Web browser and Telnetabove TCP and SNMP (simple network management protocol) above UDP as anapplication layer 24B on the other. TCP and UDP are identified by theprotocol numbers “6” and “17”, respectively, and Telnet and SNMP by theport numbers “23” and “161”, respectively. Also, the Web browser isspecified by “2001” which is a port number arbitrarily assigned by theclient.

[0068] On the other hand, the server 20A has an IP address“172.20.100.32”, and is equipped with TCP and UDP above the IP 22A as atransport layer 23A on the one hand, and HTTP and Telnet above TCP andSNMP above UDP as an application layer 24A on the other. HTTP isidentified by the port number “80”.

[0069] In accessing the Web page, the Web browser of the client 20Bcommunicates with the HTTP of the server 20A. In the process, the IPpacket 400 transmitted from the client 20B to the server 20A has theheader with the contents thereof shown in FIG. 6, for example.

[0070] The IP packet 400 includes a data field 40, a TCP header 41 andan IP header 43. The TCP header 41 includes a transmitter port number411 indicating the Web browser and a destination port number 412indicating the HTTP. Also, the IP header 43 includes a transmitter IPaddress 431 indicating the client 20B, a destination IP address 432indicating the server 20A and a protocol number 433 indicating that theapplicable protocol for the transport layer header 41 following the IPheader is TCP.

[0071]FIG. 7 shows a detailed format of the IP header 43, and FIG. 8 adetailed format of the TCP header 41.

[0072] The TCP header 41 includes a sequence number and headerinformation of other multiple items in addition to the transmitter portnumber 411 and the destination port number 412 described above. In thecase where the protocol number 433 of the IP header is “17”, the UDPheader 42 shown in FIG. 9 is employed in place of the TCP header. TheUDP header 42 also includes the transmitter port number 421 and thedestination port number 422 for identifying an application, whichconstitute a simpler header format than the TCP header.

[0073] According to this embodiment, in order that the port numberextracted from the TCP (or UDP) header of the transmission packet is setin correspondence with the class, a classification table 32 indicatedthe correspondence between the class and the port number shown in FIG.10, for example, is prepared in the QoS control information table memory30. In the classification table 32, the value of the class 322 isdefined in correspondence with the value of the port number 321applicable to the TCP header and the UDP header.

[0074] In the class determining step 1113, the classification processingunit 110 extracts the protocol number 433 from the IP header of thetransmission data (transmission packet), determines the applicableprotocol from the protocol number, and recognizing the structure of theheader of the transport layer in accordance with the applicableprotocol, reads the value of the transmitter port number 411 (or 421).Next, the classification table 32 showing the correspondence with theport number in FIG. 10 is searched for an entry in which the port number321 is coincident with the value of the transmitter port number of thetransmission data. Then, the transmission data is set in thetransmission queue 112-p corresponding to the value p of the class 322indicated by the particular entry (step 1114). In the case where thevalue of the transmitter port number 411 (or 421) is not yet registeredin the classification table 32, the transmission data is set in a queuein the default transmission queue.

[0075] The read control unit 113 reads the data from the class-wisequeue in accordance with the class-wise band assignment table 35 shownin FIG. 14, and thus realizes a predetermined QoS.

[0076] According to this embodiment, as long as the data transmissionrate of the modem 13 is not lower than a predetermined threshold value,i.e. as long as a congestion is not caused in the transmission buffer112, rapid data transmission is carried out omitting the QoS controlprocess, while in the case where the data transmission rate decreasesbelow the predetermined threshold value, on the other hand, the QoScontrol operation corresponding to the port number (type of transmitterapplication) is carried out and the transmission data is selectivelysent out. In this way, the data transmission suitable for the variationsof the information transmission rate becomes possible for the radiosection.

[0077] In a radio communication system, there may be a case in which therequired minimum network control operation such as the one defined inIEEE802.1D or the quality of the communication between specificterminals (specific connection) designated in advance is desirablyguaranteed even in the case where the information transmission rate isreduced for the radio section. In such a case, according to thisinvention, a variety of QoS control operations are made possible bypreparing a plurality of types of tables in the QoS control informationtable memory 30, as described below.

[0078]FIG. 11 shows a QoS control mode table 33 accessed to switch theQoS control mode to be executed, in accordance with the informationtransmission rate for the radio section. The QoS control mode table 33includes a QoS control mode 331 and an enable bit flag column 332 fordesignating the applicable QoS control mode in accordance with theinformation transmission rate for the radio section. In the enable bitflag column 332, the range of the information transmission rate X forthe radio section is divided into three portions including “X<lowerlimit threshold B”, “lower limit threshold B≦X<upper limit threshold A”and “upper limit threshold A≦X”. In each of these informationtransmission rate range, the applicable QoS control mode is designatedby the enable bit flag.

[0079] The QoS control mode “802.1D” determines the class according tothe priority indication label of IEEE802.1D. The QoS control mode “portnumber” determines the class according to the classification table 32shown in FIG. 10. Also, the QoS control mode “control policy Aclassification” determines the class utilizing the classification table34 showing the correspondence of the MAC address designating the class342 with the value of the MAC address 341, as shown in FIG. 12, forexample.

[0080] In the QoS control mode table 33 illustrated here, the enable bitis set to the disable state (“0”) for all the QoS control modes in thecase where “upper limit threshold value A≦X”. In the case where theinformation transmission rate X for the radio section is not lower thanthe upper limit threshold value A, therefore, the QoS control is omittedand all the transmission data are set in the default transmission queue.

[0081] In the case where the information transmission rate X for theradio section is lower than the upper limit threshold value A but notlower than the lower limit threshold value B, the QoS control mode“802.1D” and the QoS control mode “port number” are applicable. Withregard to the transmission data with the 802.1D label informationattached thereto, therefore, the class is determined from the labelinformation. For the transmission data having no 802.1D labelinformation, on the other hand, the QoS control operation is performedin such a manner as to determine the class from the classification table32.

[0082] In the case under consideration, assuming that the informationtransmission rate for the radio section is lower than the lower limitthreshold value B, the QoS control mode “802.1D” and the QoS controlmode “control policy A” are applicable. With regard to the transmissiondata with the 802.1D label information attached thereto, therefore, theclass is determined from the label information. For the transmissiondata having no 802.1D label information, on the other hand, the QoScontrol is carried out in such a way as to determine the class from theclassification table 34 of the control policy A.

[0083] In the case where a transmission packet is transmitted in theform of Ethernet frame, for example, the MAC header for Ethernetincluding the MAC addresses of the source and the destination is addedbefore the IP header of each transmission data. Thus, as for thetransmission data having no 802.1D label information, therefore, theclassification processing unit 110 analyzes the MAC header and searchesthe classification table 34 of the control policy A for an entry inwhich the address 341 coincides with the source MAC address. Once theentry involved is found, the transmission data is set in thetransmission queue 112-p corresponding to the value p indicated by theclass 342 of the particular entry. In the case where the entry involvedis not found, on the other hand, the transmission data is set in thedefault transmission queue.

[0084] For determining the class, the header information other than theMAC address and the source port number, such as the destination portnumber or the protocol type such as UDP or TCP may be used. Further, theclass for a specific terminal and a specific application can bedesignated by designating the MAC address and the port number. Also, aterminal can be recognized by an address such as the source/destinationIP address other than the MAC address, and the class of thecommunication data between specific terminals may be determined. In anycase, a classification table showing the correspondence between theheader item for determination and the class and a class-wise bandassignment table may be prepared in the memory 30, so that the relationbetween the applicable QoS control mode and the information transmissionrate for the radio section is designated by the QoS control mode table33.

[0085] The class-wise band assignment table 35 may be created each timethe corresponding QoS control mode is assigned, or different tables maybe used for different information transmission rates for the radiosection.

[0086] In the case where the QoS control information table memory 30 isconfigured of a nonvolatile memory such as NVRAM, the various tables 31to 35 described above are written in the memory 30 before shipment ofthe radio transmitter/receiver. Also, updated data are supplied to theparticular radio transmitter/receiver in the form of the control messagetransmitted from a device such as a maintenance PC and then written inthe memory 30 by the maintenance software prepared in the control unit20, as required.

[0087] In the case where the memory 30 is configured of a volatilememory such as a RAM, for example, the table contents constituting amaster table are written in a ROM or a nonvolatile memory of the controlunit 20, and when the radio transmitter/receiver is powered on, thecontents of the master table are copied automatically to the memory 30.Alternatively, when power is switched on, the radio transmitter/receiverautomatically communicates with the maintenance PC, so that the controlunit 20 writes the table contents downloaded from the maintenance PCinto the memory 30. According to the latter method, the functions ofeach radio transmitter/receiver can be readily changed even in the casethe applicable QoS control mode or the table contents undergo a change.

[0088] Next, the radio transmitter/receiver according to anotherembodiment of the invention will be explained with reference to FIG. 16.

[0089] According to this embodiment, there is provided a radiotransmitter/receiver combined with the adaptive modulation, in which theQoS control operation according to the invention is performed byestimating the conditions of the transmission path based on the receivedpower or the bit error rate detected when the radio signal with an errorcorrection code added and modulated by a selected modulation scheme atthe transmitting end is demodulated with the error corrected at thereceiving end. In accordance with the estimated transmission pathconditions, an appropriate modulation scheme is selected from 64 QAM(64-positions quadrature amplitude modulation), 16 QAM (16-positionsquadrature modulation), QPSK (quadrature phase shift keying) and BPSK(binary phase shift keying).

[0090]FIG. 16 is a block diagram showing a configuration of a radiotransmitter/receiver according to an embodiment of the invention. Thisradio transmitter/receiver comprises a QoS control unit 11-2, a radioframe coding unit 12-1, a modulation unit 13-1, a transmission RF unit14-1, a multiplexer 14, an antenna unit 15, a receiving RF unit 14-2, ademodulator 13-2, a radio frame decoder 12-2 and a propagation pathestimation unit 11-1.

[0091] The overall operation of the radio transmitter/receiver will beexplained. The order in which the transmission data is transmitted ischanged by the QoS control unit 11-1, and the transmission data isdivided into frames by the radio frame coding unit 12-1, whereby a errorcorrection code, a training bit and a guard bit are added to produce aradio transmission frame. This radio transmission frame is modulated bya predetermined modulation scheme at the modulation unit 13-1, convertedinto a radio frequency at the transmission RF unit 14-1, and through themultiplexer 14, transmitted into space by way of the antenna unit 15. Inthe receiving operation, on the other hand, a radio signal is receivedfrom the antenna unit 15, and the received radio signal is convertedinto a baseband signal at the receiving RF unit 14-2 through themultiplexer 14. This baseband signal is demodulated at the demodulationunit 13-2 by a demodulation scheme corresponding to the predeterminedmodulation scheme, and the demodulated data is decoded with the errorcorrected at the radio frame decoder 12-2 thereby to produce thereceived data. The propagation path estimation unit 11-1 estimates thepropagation path conditions from the output signal of the demodulator13-2, and selecting the optimum modulation scheme, designates themodulation scheme for the radio frame coding unit 12-1 and themodulation unit 13-1.

[0092] Next, a method of switching the modulation scheme constituting afeature of the invention will be explained.

[0093]FIG. 17 shows an example of a FWA (fixed wireless access) systemconfiguration according to the invention, in which the datacommunication between stations is realized by P-P (point-to-point)connection between a base station and a terminal station.

[0094]FIG. 18 is a diagram for explaining the process of connecting abase station and a terminal station by P-P connection. After resettingby switching on power, the base station starts the transmission of async code while at the same time starting to capture the synchronizationfor the receiving operation. The terminal station also starts to capturethe synchronization for the receiving operation. Once the receivingsynchronization is established, the terminal station starts thetransmission of the sync code. The base station, upon establishment ofthe receiving synchronization, starts the data transmission using thedata transmission frame. The terminal station, upon receipt of the datatransmission frame, executes the data receiving process, while at thesame time starting the data transmission using the data transmissionframe. The modulation scheme for the sync frame and the datatransmission frame is predetermined between the base station and theterminal station. By starting the communication in this way,synchronization is established between the base station and the radiostation thereby to start the transmission/receiving of the dataaccording to the predetermined modulation scheme.

[0095] Next, an explanation will be given about the operation ofswitching the modulation scheme by adaptive modulation after startingthe data communication. The adaptive modulation is for realizingefficient communication by switching the modulation scheme in accordancewith the propagation path conditions. The parameters for estimating thepropagation path generally include the receiving level, the residualerror and the bit error rate. This technique is described, for example,in JP-A-10-93650, and “Symbol Rate and Modulation Level-ControlledAdaptive Modulation/TDD System for High-Bit-Rate Wireless DataTransmission” by Toyoki Ue et al., IEEE Trans. on Vehicular Technology,Vol. 47, No. 4, November 1998, which is hereby incorporated byreference. In this embodiment, reference is made to a case in which thepropagation path conditions are estimated using the receiving level bythe propagation path estimation unit 11-1. The propagation pathestimation unit 11-1 regularly receives the receiving level informationof the receiving signal from the demodulator 13-2, and by referring tothe receiving level-vs-modulation scheme correspondence table shown inFIG. 19, selects a corresponding modulation scheme, and notifies thecode indicating the selected modulation scheme to the QoS control unit11-2, the radio frame coding unit 12-1 and the modulation unit 13-1.

[0096] The radio frame coding unit 12-1, in producing a datatransmission frame, generates a radio frame containing the codeinformation indicating the modulation scheme notified by the propagationpath estimation unit 11-1.

[0097] The modulation unit 13-1 reads the code indicating the modulationscheme notified from the propagation path estimation unit 11-1 for eachframe processing, and in the case where the code indicating the notifiedmodulation scheme is different from the currently-used modulationscheme, the modulation scheme is changed from the next frame. At thereceiving end, on the other hand, the information indicating themodulation scheme is separated from the data transmission frame aftererror correction decoding at the radio frame decoding unit 12-2 andnotified to the demodulator 13-2. In the case where the information onthe modulation scheme notified to the demodulator 13-2 is different fromthe modulation scheme corresponding to the currently-used demodulationscheme, the demodulator 13-2 changes the demodulation scheme from thenext frame.

[0098] An example of the data transmission frame format is shown in FIG.20. The data transmission frame is configured of a training bit (TRN)for timing synchronization, a block (RCB: radio control block) for theinformation indicating the modulation scheme (MODTYPE) and themaintenance information, a block (DTB: data traffic block) for storingthe data traffic and a guard bit for separating the frames. The radioframe coding unit 12-1 notifies the remote station of the modulationscheme by setting the modulation scheme to MODTYPE. The RCB is notrequired to be transmitted for each frame but several frames, ortransmitted when switching the modulation scheme, while DTB may betransmitted in other cases. The sync code may be a bit train withscrambled 0s.

[0099] In the propagation path estimation unit 11-1, a modulation schememay be selected using the time average value of the receiving level asrequired in order to absorb the receiving level variations. Also, thepropagation path estimation unit 11-1 can be configured in such a manneras to estimate the propagation path using the result of error correctiondecoding at the radio frame decoding unit 12-2.

[0100] An embodiment in which the P-P connection is employed between abase station and a terminal station is described above. Nevertheless,this invention is applicable also to the P-MP (point-multipoint)connection between a base station and terminal stations with equaleffect.

[0101] According to this embodiment, a radio base station is preferablyinstalled at a line-of-sight place or a place of unobstructed view. Inorder to avoid the effect on the base station in operation, however, theplace of installation is required to be determined after careful study.Even in the case where the base station is installed at a sufficientlystudied place, however, the effect on other base stations may berevealed only after actual installation of the particular base stationat the particular place. In such a case, the base station or thesubscriber station is equipped with devices for the current system andthe spare system, and the operation is switched to the device for thespare system in compliance with a control instruction from a managementcenter or the like. In this way, the radio communication environment ofthe system can be optimized and the continued communication service ismade possible. A radio communication system equipped with a radiotransmitter/receiver for the current system and the spare system isdisclosed in JP-A-2002-94449.

[0102] Embodiments of the invention are described above with referenceto the packet transmission using TCP/IP as an example. Nevertheless, theconcept of the invention is not limited to the communication protocolspecified in the aforementioned embodiments but applicable to otherprotocols with equal effect.

[0103] The read control method is also not limited to the token bucketscheme, but applicable to various schemes including those for readingthe transmission data in the descending order of priority from a queuecorresponding to a class of high priority.

[0104] It will thus be understood from the foregoing description thataccording to the embodiments described above, the requirement or norequirement of the QoS control is determined in accordance with theinformation transmission conditions in the radio section thereby toselectively execute the QoS control operation. As compared with the QoScontrol operation according to the conventional scheme executed all thetime, therefore, the transmission delay time of the transmission datacan be shortened for an improved throughput. Also, by employing a methodof changing the applicable QoS control mode in accordance with theinformation transmission conditions in the radio section with referenceto the QoS control mode table, the data transmission keeping up flexiblywith the radio environment is made possible.

[0105] It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

What is claimed is:
 1. A quality of service (QoS) control system usedfor a radio transmitter/receiver, comprising: a QoS control unit forsupplying the modulator of said radio transmitter/receiver with thetransmission data in the order taking the QoS into consideration; and adetermining unit connected to said QoS control unit for determiningwhether the QoS control operation of the transmission data is requiredor not in accordance with the information transmission conditions in theradio section; wherein the QoS control operation of the transmissiondata by said QoS control unit is performed selectively in accordancewith the information transmission conditions in the radio section.
 2. AQoS control system according to claim 1, wherein said QoS control unithas a first operation mode for outputting said transmission data in theorder of input and a second operation mode for outputting saidtransmission data in the order taking the QoS into consideration, saidfirst and second operation modes being switchable to each other inaccordance with the information transmission conditions in said radiosection.
 3. A QoS control system according to claim 2, wherein said QoScontrol unit includes a comparator for comparing said informationtransmission rate for said radio section with a predetermined thresholdvalue, said QoS control unit being switched to said second operationmode in the case where said information transmission rate for said radiosection is lower than a predetermined threshold value, said QoS controlunit being switched to said first operation mode in the case where saidinformation transmission rate for said radio section is not lower thansaid predetermined threshold value.
 4. A QoS control system according toclaim 3, wherein said QoS control unit has a queue unit for outputtingsaid transmission data in the order of input in said first operationmode.
 5. A QoS control system according to claim 3, wherein said QoScontrol unit has a class-wise queue unit for setting the transmissiondata in a queue in accordance with the class of said transmission datain said second operation mode.
 6. A QoS control system according toclaim 5, wherein said QoS control unit includes a class-wise bandassignment table for setting a guarantee band for each class and a readcontrol unit for reading the transmission data from said class-wisequeue unit in accordance with said class-wise band assignment table. 7.A QoS control system according to claim 1, wherein said informationtransmission rate for said radio section is obtained from theinformation on specific bits contained in the received data.
 8. A QoScontrol system according to claim 1, wherein said QoS control unit has aplurality of QoS control modes, and wherein the QoS control modeapplicable to the transmission data is switched between said pluralityof said QoS control modes in accordance with the informationtransmission rate for said radio section.
 9. A QoS control systemaccording to claim 8, wherein said QoS control unit has a QoS controlmode table for defining the relation between the range of thetransmission rate for said radio section and the QoS control modeapplicable to the transmission data, and wherein said QoS control modeapplicable to the transmission data is determined in accordance with theinformation transmission rate for the radio section with reference tosaid QoS control mode table.
 10. A QoS control system according to claim8, wherein said QoS control unit has a classification table showing thecorrespondence between the class and a specific QoS control mode definedby said QoS control mode table, and wherein said classification tabledefines the class of each transmission data corresponding to the valueof specific header information contained in said transmission data, andwherein said QoS control unit determines the class of the transmissiondata in said specific QoS control mode with reference to saidclassification table.
 11. A QoS control method for a radiotransmitter/receiver, comprising: a first step of determining whetherthe QoS control of the transmission data is required or not inaccordance with the information transmission conditions in the radiosection; a second step of supplying the transmission data to themodulator of said radio transmitter/receiver in the order taking the QoSinto consideration in the case where said QoS control operation isrequired; and a third step of supplying the transmission data to saidmodulator in the order of input in the case where said QoS controloperation is not required.
 12. A QoS control method for a radiotransmitter/receiver according to claim 11, wherein said second stepincludes the steps of determining the class of each of said transmissiondata, setting said transmission data in a class-wise queue correspondingto a determined class, and reading the transmission data from saidclass-wise queue in accordance with a class-wise band assignment tablewith a guaranteed band set for each class.
 13. A radiotransmitter/receiver comprising: an adaptive modulation-typetransmission unit connected to an antenna; and a receiving unitconnected to said antenna; wherein said adaptive modulation-typetransmission unit includes: a high frequency unit connected to saidantenna; a modulation unit connected to said high-frequency unit; aradio frame coding unit connected to said modulation unit for convertingthe transmission data into a format of a modulation scheme correspondingto the propagation path conditions in the radio section; and a QoScontrol unit for supplying the transmission data to said radio framecoding unit in order taking the quality of service (QoS) intoconsideration.
 14. A radio transmitter/receiver according to claim 13,further comprising a propagation path estimation unit for estimating theconditions of the propagation path for the radio section from the signalreceived by said receiving unit.
 15. A radio transmitter/receiveraccording to claim 14, further comprising a modulation-type selectingunit connected to said propagation path estimation unit for selectingone of a plurality of modulation schemes.
 16. A radiotransmitter/receiver according to claim 15, wherein said plurality ofthe modulation schemes include 64 QAM, 16 QAM, QPSK and BPSK.
 17. Aradio transmitter/receiver according to claim 13, wherein said receivingunit includes means for extracting the information on the modulationscheme of the received data from said received data.
 18. A fixedwireless access (FWA) system comprising: a radio base station; and aplurality of subscriber stations adapted to communicate with said basestation by radio; wherein selected one of said radio base station andsaid subscriber stations includes a radio transmitter/receiver accordingto claim 13.